Third, Nanjing Second Bridge on the sub-project, unit project and overall construction schedule
The construction of the second Yangtze River Bridge in Nanjing will be approved by the state for 4 years. The Nanxun Bridge and the South Bank lead were started in 1997. The Beibei Bridge and the Approach Bridge and the Nanxun Bridge Approach Bridge. The Baguazhou Lead and North Leads were started construction in 1998. The Nanjing Second Bridge will be completed and opened to traffic in July 2001. The total construction period is 45 months. The south and north main bridges of the Nanjing Second Yangtze River Bridge are constructed in accordance with five sections, as follows: the construction of the South Tower Bridge and the foundation project is A, the construction period is 24 months, and the upper structure of the Nantun Bridge is B. The planned construction period is 15 months, the south approach bridge of Nanxun Bridge is C standard, the planned construction period is 28 months, the south approach bridge of Nanxun Bridge is D standard, the planned construction period is 30 months, and Beibei Bridge and its approach bridge are E standard. The planned duration is 30 months. See the schedule of work schedule for details. |
Fourth, the key points and difficulties of the Nanjing Second Bridge Project
The main points of quality control of Nanjing Second Bridge Project are steel box girder cable-stayed bridge--Nanjing Bridge, prestressed concrete continuous girder bridge--Beibei Bridge and lead-modified asphalt pavement and Nanqiaoqiao steel bridge deck pavement.
The difficulties in the construction of Nanjing Second Bridge can be divided into the following categories:
1. Deep water foundation construction on the main channel of the Yangtze River: large-diameter double-wall steel cofferdam anchoring location, suction rock; 8m thick underwater concrete bottom construction; super long and large diameter bored pile construction; large-volume concrete hydration Thermal control.
2 inverted Y-type tower super high-altitude concrete pouring, large curvature and small radius circumferential prestressed construction, spatial cable stay sleeve positioning.
3. Flat streamlined steel box girder fabrication, suspension and steel bridge deck epoxy asphalt pavement.
Construction control of 4.628m span cable-stayed bridge construction and 165m span prestressed concrete continuous beam.
5. Underwater foundation construction of weak foundation on the Yangtze River auxiliary channel; construction of bored pile of Beibei Bridge.
6. Technical countermeasures, quality control of soft soil roadbed and durability study of asphalt pavement.
V. Practice and experience of construction and management of Nanjing Second Bridge Project
The Nanjing Second Bridge project is grand in scale and tight in schedule. It involves a wide range of professions, high technical difficulty, high construction risks and arduous construction tasks. The Nanjing Second Bridge Construction Command adopted the following measures for the quality control and control of the Second Bridge during the construction of the Second Bridge:
Strict project legal person system, give full play to the organization and coordination role of project legal person system in project management, take various measures, and firmly grasp the initiative of engineering construction. At the beginning of the construction of Nanjing Second Bridge, combined with the specific situation of the Nanjing Second Bridge Project, carefully formulate the overall implementation plan of Nanjing Second Bridge, reasonably arrange the construction period and the connection of various processes, clarify the control objectives of quality, progress and investment in each stage, and always grasp the project construction. Initiative. In the process of project construction, no matter the organization and coordination of the construction, or the problems and social contradictions that arise during the construction, the commanding department, as the dispatching agency of the owner, does not push the committee and does not arbitrarily, and gives full play to the leading role of the project legal person. The government's administrative means are used to ensure that the project has a good external environment and the project is implemented smoothly. It also relies on the second-level supervision organization to strictly control the quality, progress and investment of the project. The following measures have been taken in this regard:
1. Break the routine and make a double-walled steel cofferdam in advance. In the underwater foundation construction of the Nanqiao main bridge in Nanjing Second Bridge, the steel cofferdam used for the foundation construction water-retaining facilities has a diameter of 36m and a height of 65m. It is currently the largest construction water-retaining facility in China. Several Yangtze River Bridges that have been built and under construction in China are completed by the construction unit after the arrival of the steel cofferdam. However, the headquarters decided decisively according to the actual situation of the Second Bridge. The command department broke the routine and separately tendered the production of steel cofferdams as an independent tender in May 1997, thus ensuring that the provincial and municipal governments requested the substantive commencement in October 1997. The goal is achieved. What's more important is to win a precious five months for the construction period of Nanxun Bridge, and to implement the process of sinking rock and sealing the steel cofferdam in the dry season from 1997 to 1998. The safety of the deep water foundation of the Nanxun Bridge in the year was created by the extraordinary floods in 1998. If the steel cofferdam is not processed in advance, in the face of the 1998 flood, the steel cofferdam can be safely smashed, and the result is unimaginable.
2. Adhere to major construction plans and process review. As a project legal person, the command department strengthens the organization and control of the project. For major construction plans and processes, the construction unit is strictly required to apply for the construction plan in advance. The major construction plans and processes are also reviewed by the headquarters to organize the relevant experts for construction. The unit prepares for the process conversion in advance. For example, in the construction of the steel cofferdam, we invited the Zhouqiao troops to participate in the discussion of the plan, which provided guarantee for the feasibility of the plan; before the construction of the cable tower, an expert seminar was held on the construction of the cable tower, and the steel box beam production process was carried out. In the middle, we will do a good job of the fatigue test of the anchor box under the cable stayed in advance, and determine the construction process and plan, so that the construction unit can do all the preparatory work in advance according to the determined plan, shorten the process conversion time and improve the organization of the project. The construction risk is greatly reduced.
3. Combine the actual situation of the second bridge project, reasonably arrange each process, in order to obtain the double effect of guaranteeing the construction period and saving investment. In order to overcome the late subsidence of the eight-cluster lead soft soil roadbed and ensure the stability of the roadbed, the construction of the Bafengzhou subgrade will be carried out in advance. According to the construction drawing design documents, the project can be scheduled to start construction in 1999, but the headquarters considers the construction through advanced roadbed construction. In combination with technical measures, the settlement of soft soil roadbed is completed as much as possible during the construction period to reduce the post-construction settlement of the upper roadbed. The extraordinary soft soil foundation of Bafengzhou is more than 20 meters deep, and the settlement of the roadbed is large at the late stage. Building materials and advancing roadbed construction, using time to preload is the most effective and economical measure to solve the settlement and stability of the roadbed later. The headquarters decided to start the roadbed filling in early 1998 and use the preloading for more than one year. To solve the problem of subgrade settlement, good results have been achieved.
4. Rely on technology, be brave in technological innovation, and ensure construction progress and quality. During the construction process, the headquarters pays attention to optimizing the construction process and adopting practical technical measures to grasp the initiative of the project. For example, if the steel cofferdam rock is changed into rock, it will win two months in one fell swoop; the deep water foundation bored pile construction will shorten the pile length and change the mud wall drilling hole into clear water drill through the test, which not only accelerates the construction progress but also ensures the construction progress. The quality of the project; in addition, 5 active cross braces are used in the construction of the tower column in the tower, which accelerates the construction progress on the basis of ensuring the quality of the project and improving the structural stress.
Carefully prepare the bidding and management documents, strictly implement the project bidding system, and select the first-class units to participate in the construction of the second bridge. Before the implementation of the project, we will make the selection of good teams as an important task for us. Because the main body of engineering quality is the design and construction unit, the extraordinary construction unit, the overall quality awareness, the level of governance will directly affect the quality and progress of the project. In order to standardize and procedurize the entire bidding process of Nanjing Second Bridge, the command department firstly combines the relevant regulations such as the Ministry of Communications, the Jiangsu Provincial Communications Department, the bidding and tendering regulations, the highway construction currency control method, and the Nanjing Municipal People's Government Order. Based on the principle of the division of the Nanjing Second Bridge Project, the “Measures for the Construction of the Nanjing Yangtze River Second Bridge Construction Project Tendering†and the “National Changjiang Second Bridge Construction Project Target Bottom Preparation and Governance Measures†were formulated. Secondly, our department commissioned a professional design consulting unit, in accordance with the relevant national laws and regulations, combined with the actual situation of the second bridge project, consider factors such as the integration with international practices. A set of bidding documents was carefully prepared and approved by the Ministry of Communications. It is clear that the main body is not allowed to subcontract or subcontract, the joint bidding is not allowed, the anti-bribery clause is added, and the low-price bidding is opposed. The project manager of the important bidding section clearly puts forward strict requirements in the bidding documents, and requires the project manager to leave the construction site to leave the command and the director, and the replacement project manager must obtain the consent of the command. In the bidding process, we insisted on following the prescribed procedures, insisting on selecting the best team, not advocating or disapproving the low-price bid, resisting the human condition, saying the situation, and not implementing local protectionism. Conduct disciplinary inspection and notarization participation in the whole process to ensure “openness, fairness and justiceâ€. On the basis of the clearing of the headquarters, experts are invited to evaluate the bids, and finally, the bidding committee will discuss and adopt the unscheduled voting standard. Through strict bidding, we have selected the design unit, construction unit and supervision unit of the South and North Bridge. The practice of nearly three years has confirmed that our design, construction and supervision units have not selected the wrong ones, which guarantees the quality and progress of the project.
Carry out the project supervision system, establish a two-level supervision system according to the international FIDIC terms, national conditions and the actual situation of Nanjing Second Bridge, and hire construction supervision with rich construction experience. According to years of engineering practice, the command department carried out bold innovations in the project supervision organization system, established and improved the principle of “two-level supervision, and formulated a number of quality awards and punishments. According to the spirit of the Provincial Communications Department on quality and excellence. Set up a special quality award fund, give spiritual and material rewards to units that value quality, give approval and economic punishment to units that despise quality control and chaotic engineering governance, and form quality, pursuit of perfection and excellence in “one bridge and four parties†Good atmosphere. For example, at the Nanxun Bridge Bored Pile Construction Mobilization Conference, the special quality award and the Sota Construction Mobilization Conference proposed the “Analine Bridge A-standard Section Cable Tower Construction Quality and Construction Period Control Award Assessment Methodâ€, the headquarters promised The investment of each construction unit to ensure the quality of the project will be rewarded and compensated according to the principle of “high quality and good priceâ€. The construction of the Nanjing Second Yangtze River Bridge also requires the quality of the construction of the second bridge – the quality of the construction unit The wage system further increases the proportion of wages in the wages of workers, and forms an emphasis on quality and Good atmosphere and mechanisms for quality.
In addition, during the construction of the Second Bridge, the headquarters promised that any unit and individual would provide support and encouragement for suggestions for improving and ensuring quality. When rationalizing suggestions for improving construction quality and confirming by the expert committee, the headquarters will regard the actual situation. The situation is given appropriate rewards. Similarly, the construction units that have failed to meet the requirements of the command plan for the quality of the project and the progress of the project will never let go, and truly unselfish in quality issues. For example, a construction unit of Beibei Bridge of Nanjing Second Bridge could not meet the requirements of the headquarters because of the construction of the second bridge. Although it was the construction unit within the system of the Ministry of Communications, the headquarters still cleared the scene and selected a non-traffic through bidding. The construction unit of the system continues to undertake construction tasks.
Engineering quality management is a systematic project. The quality of the owners, the unity and cooperation of the bridge and the square, and the good external environment are also important links to ensure the quality of the project. The headquarters created a good construction environment for the units involved in the construction of the Second Bridge. At various meetings, the headquarters clearly stated to the units that the obligations of Party A are stipulated in the contract, and we have done it decisively; The command can do it, and we also strive to do it, and play the leading role of the project legal person everywhere. We make full use of the construction headquarters as the special agency for the construction of the second bridge dispatched by the government, and actively coordinate all aspects of the relationship so that the construction units can concentrate on construction. For example, in the construction of the steel cofferdam, the key to success is the supply and organization of underwater concrete. The command headquarters will coordinate and arrange the pontoon bridge of the Nanjing Military Region to set up the pontoon bridge to take the amphibious water supply to the underwater concrete. The port supervisory, waterway, power supply, meteorological and other departments have done a good job of coordination and service, so that the pouring strength of the sealing concrete reaches 200m3/h, which ensures the quality of the concrete at the back cover.
On the basis of factors such as inconvenient transportation, the Second Bridge Construction Headquarters has established a land-based concrete mixing station on the Baguazhou to ensure the construction of the North Tower and the construction quality of the Baguazhou lead, thus ensuring the pouring amount of the back cover concrete. The concrete quality of all structures of the Baguazhou lead. During the construction of the South Tower's back cover, in order to repair the construction road, the headquarters also designated the construction machinery and construction materials of the special organization to support the Hunan Road and Bridge, and won the time for the construction of the South Tower. These are the practical actions of the command department to create a good construction environment and provide quality engineering services.
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