What is the specific content of safety management in subway tunnel shield construction? The following is the answer of Zhong Da Consulting Company.

1 Introduction Safety management has been paid more and more attention in China. Especially after China's entry into WTO, the global economy tends to be integrated, which requires developing countries to catch up with the world's advanced level in safety production management. Enterprise safety management has been regarded as an important content of enterprise management alongside production management. The construction industry is an industry with frequent casualties, second only to mining operations. Tunnel construction has some common characteristics with the construction industry and mining industry, with great construction risks and many hidden dangers. Shield tunneling technology is an advanced tunnel construction technology. The excavation face is protected by shield, which can avoid personal injury and death accidents caused by soil instability or roof caving to the maximum extent. In recent years, it has been widely used in Shanghai, Guangzhou, Beijing and Shenzhen. Shield tunneling technology was invented by British engineer Bruner in 18 18, and was applied to engineering practice in 1825. China introduced shield construction technology from 1956, which has developed rapidly since 1980s. At present, it has gradually become the mainstream way of subway construction in Shanghai, Guangzhou and other big cities, and its unique safety construction and management problems have aroused widespread concern. This paper is a summary of shield construction practice and safety management experience for many years. 2. Pneumatic operation in front of the cutter head of the shield machine 2. 1 Pneumatic operation of the shield machine When the operator must enter the cutter head of the front body of the shield machine, if the soil in front of or above the shield machine cannot stabilize itself, the upper body may enter the cutter head through the opening of the cutter head, threatening the safety of the operator. Most advanced shield machines are equipped with air compression system, that is, oil-free air is injected into the cutter head by sealing the passage between the cutter head and the shield precursor, so as to increase the pressure in the cutter head and balance the external earth pressure, and the maximum pressure can reach 3-4kg/cm2. In order to ensure the adaptability of operators, a closed transition plenum is generally set in the tunnel, which will greatly reduce the influence of pressure change on operators. Because the operator works in a closed environment and the space in the cutter head is narrow, many people can't work at the same time. The air quality may also contain some impurities, and the ambient temperature of the working face will be very high. When the operator is uncomfortable, it takes some time to decompress and transition before he can go to the hospital. Therefore, compressed air operation is a key point of shield construction and a dangerous source worthy of attention. 2.2 Corresponding measures for air compressor operation (1) Try to reduce the entry into the cutterhead under adverse geological conditions, and try to open the cabin in the basically self-stable stratum without air compressor operation. Therefore, according to the change of geological conditions, we should choose the appropriate time to advance or postpone the entry into the cutter head, especially when replacing the cutter. (2) Choose healthy and strong workers as operators to enter the cutter head, and carry out strict physical examination in the occupational disease hospital to ensure the resistance to harsh environment. Under normal circumstances, compressed air operation should not exceed 4 hours a day. (3) If an air compressor is needed, an oil-free air compressor must be selected to ensure air quality and reduce environmental pollution. (4) Prepare communication tools and keep in touch without interruption. (5) Make emergency preparations, rescue the wounded in the decompression chamber (the sealed transition passage between the cutter head and the shield precursor) when necessary, and sign a first aid agreement with relevant hospitals. If conditions permit, it is necessary to equip a special mobile medical cabin, so that the external pressure difference suffered by the wounded in the process of being sent to the hospital is basically the same. 3 Shield cutter replacement With the change of geological conditions, the cutter needs to be replaced during tunnel excavation, especially when the rock strength is high, the hob needs to be replaced. Generally, hob is back-unloading, which is convenient for disassembly, but relatively speaking, hob is relatively heavy, smooth around, and has no fixed point, so it is difficult to carry, and the installation and disassembly are much more difficult than scraper and cutter. The space in the cutter head is narrow, so it is difficult for many people to work at the same time and it is difficult to use machinery. Often, the cutter head is slippery, and the lower part of the cutter head is full of mud or mud. Unstable rock and soil may fall into the opening of the cutter head, which will affect the tool change. Therefore, changing the cutter head is a dangerous process, and many construction units sometimes have minor accidents and major accidents when changing the cutter head. When replacing tools, the following matters should be noted: (1) When the geological conditions are not good and the stratum on the excavation surface may be unstable, the stratum should be reinforced in advance, and grouting or support can be adopted in the hole to prevent the rock and soil from hurting the operators, especially when the operators are hit by unexpected objects during the tool handling, and it takes a long time to salvage the tools; What's more, people are easily injured by the hob, and may even slide to the bottom of the cutter head and be injured by the hob for the second time, resulting in serious consequences. (2) In addition to taking necessary measures for the stratum, other preparations should be made, such as cleaning up the accumulated soil or silt and mud in the cutter head, keeping the working space in the cutter head as much as possible, setting up a stable temporary support and working platform, and providing sufficient lighting, including local lighting tools such as traveling lights. (3) Choose skilled, hard-working and healthy workers to change tools, especially to cooperate with each other skillfully, so as to shorten the downtime of the shield machine as far as possible and prevent soil instability. If the soil is seriously unstable, the tool change can be completed several times. Generally, the strength of soil is not very strong at this time, so the shield machine can be opened several times before replacing another batch of tools. The stay time of shield machine in soft soil stratum should not exceed two days. (4) Hob is heavy and smooth, so it is not suitable for fixing. Therefore, they should be installed and removed with the help of mechanical equipment as much as possible. For example, lifting devices such as cranes and slide rails, and fixing devices such as brackets should be used reasonably, and be careful when operating. (5) The cutter head is wet and full of water, which will cause atomization with the increase of temperature. It requires high insulation performance of electrical appliances and wires, so it is necessary to choose safe voltage below 24V. (6) In the process of shield construction, injuries caused by unexpected rotation of cutter head occur from time to time. Therefore, when restarting the shield machine, it is necessary to repeatedly confirm that there are no operators in the earth warehouse and all the tools and materials have been recovered. It is best to realize the essence of safety, that is, lock the control switch in the original operation room, add the control switch at the entrance and implement the system of repeated listing and counting.

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