"It is reported that the E6-B section steel end shell panel is uneven by 3 mm, and the unevenness within each linear meter is 1 mm, and the construction quality reaches the expected target." With a series of reading reports from the staff of the Yuliangzhou Cross-River Tunnel project on the east-west axis of Xiangyang built by the Second Aviation Bureau, a warm cheer sounded at the construction site of the waterwork area located on the han river.
The steel end shell is the base surface of the waterstop and immersed pipe installation, which acts like the foundation of a building. Because the waterstop belt relies on compression to stop water, if the base surface is uneven, then it will be unevenly stressed when facing another base, affecting the water stopping effect. Therefore, the elevation, accuracy and flatness requirements of steel end shell panel welding are extremely stringent.
According to the design requirements, the unevenness of the steel end shell panel should be controlled within 3 mm after installation. However, in the actual construction process, affected by welding deformation, span length at both ends and concrete pouring pressure in the later stage, the overall installation accuracy of its components is extremely difficult to control, and the control standards of the same type of construction project require 5 mm.
"It must be controlled at 3 mm, and only by reaching 3 mm can we ensure the compression strength of our immersed pipe waterstop and achieve water leakage." What's the problem with 3mm that we can't solve? Why can't I control it? At the request of Sun Xiaowei, the project department held a special technical seminar, and the welding worker master split the entire welding installation process in detail. Everyone found the crux of the problem: "The span at both ends reaches 30 meters, according to the traditional positioning method and control means, usually the baffle is only placed at 1 meter interval, so that the strip structure welded upwards is separated by 1 meter to have a fixed place, then the entire middle piece is actually free, and the error is large." ”
"Since we're going to control a straight line, let's pull a straight line first." The project department plans to first use the measuring instrument to determine the installation line of the panel, use the steel wire directly from the two ends of the 30 meters to pull into a straight line, and then according to the installation line, the end of the steel shell panel is installed in place in accordance with the order from the middle to the sides, from the bottom to the top, so that when the steel plate is placed upwards, in addition to the spaced baffle, it is only necessary to see whether the free place in the middle can be aligned with the steel wire, if it is not aligned, it means that the number of steel plates placed is not enough, so repeated verification, repeated encryption, improve accuracy.
After clarifying their thinking, the big guys were more confident and immediately practiced. However, the first attempt hit the wall, and then reworked three or four times, the installation accuracy still could not meet the design requirements, the reason is that the battle line is too long, although the number of partitions has increased, but the corresponding points that need to be adjusted have also increased.
Reinvigorating, the project department once again held a special meeting on the installation of steel end shell panels. After repeated analysis and discussion, the project department decided to start from the positioning method and measurement method to optimize, on the one hand, the original one-time welding method was changed to indirect jump welding and layered welding, first from the lower end of the side wall to the middle of the bottom plate in sequence construction, and then from the side wall to the top plate closer, each panel welding completed the acceptance of acceptance, and then the next panel welding to avoid panel deformation, to ensure the quality of panel welding; on the other hand, the use of a higher precision total station measurement, and with a card code for fine adjustment. In addition, the project department also innovated and invented a magnetic 360-degree prism, so that it is adsorbed on the panel, realizing 360-degree all-round accuracy measurement, and monitoring the deformation of the panel at any time to improve the measurement accuracy.
"Starting from the whole, no matter how the control accuracy will be affected by deformation, then what we have to do is to fine control each steel end shell panel, so that each steel end shell panel will achieve zero error when initially positioned, and ensure that the error of the finished product only exists in the heat deformation caused by the welding, so that the deformation of the entire steel plate will not be too large." Sun Xiaowei said.
The results were immediate. On December 24, 2019, the first steel end shell panel was successfully installed, and on May 24, 2020, all the steel end shell panels in the Dongfen Work Area were installed, and the monitoring data showed that the error was only 3 mm, and some were even only about 1 mm, which made everyone at the scene excited.
"Excellence, quantitative change produces qualitative change, as long as one of the points can be done well, then the project can become better!" Sun Xiaowei said.
source
Traffic Construction Newspaper
Second Aviation Bureau
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